tert_butyl-methyle-eng.pdf

Canadian Environmental
ProtectionAct
Priority Substances List
Assessment Report No. 5
Government
of Canada
Environment
Canada
Health
Canada
Gouvernement
du Canada
Environnement
Canada
Santé
Canada
Methyl butyl Ether
tertiary-
Canada CANADA'S GREEN PLAN

Canadian Environmental Protection Act
PRIORITY SUBSTANCES LIST
ASSESSMENT REPORT No. 5
METHYL tertiary-BUTYL ETHER
Government of Canada
Environment Canada
Health and Welfare Canada
Also available in French under the title:
Loi canadienne sur la protection de l’environnement
Liste des substances d’intérêt prioritaire
Rapport d’évaluation n°. 5
Oxyde de tert-butyle et de méthyle

CANADIAN CATALOGUING IN PUBLICATION DATA
Main entry under title:
Priority substances list, assessment report no. 5,
methyl tertiary-butyl ether
At head of title: Canadian Environmental
Protection Act.
Issued also in French under title: Liste des
substances d’intérêt prioritaire, rapport
d’évaluation n0
5, oxyde de tert-butyle
et de méthyle.
Includes bibliographical references.
ISBN 0-662-19941-3
DSS cat. n. EN40-215/5E
1. Butyl methyl ether. 2. Butyl methyl ether --
Toxicity testing. 3. Environmental monitoring - -
Canada. I. Canada. Environment Canada.
II. Canada. Health and Welfare Canada.
TD196.B87P74 1992 363.73’84 C92 - 099764 - 3
©Minister of Supply and Services Canada 1992
Catalogue No. En 40-215/5E
ISBN 0-662-19941-3
BEAUREGARD PRINTERS LIMITED

Methyl tertiary-butyl ether
iii
TABLE OF CONTENTS
Overview of Findings ...........................................................................................................v
1.0 Introduction..............................................................................................................1
2.0 Summary of Critical Supporting Data...................................................................4
2.1 Identity and Physical/Chemical Properties of Substance...............................4
2.2 Production and Uses.......................................................................................4
2.3 Sources and Releases .....................................................................................5
2.4 Environmental Fate and Concentrations ........................................................5
2.4.1 Fate ....................................................................................................5
2.4.2 Concentrations...................................................................................5
2.5 Toxicokinetics and Metabolism.....................................................................6
2.6 Mammalian Toxicology.................................................................................7
2.7 Effects on Humans .........................................................................................8
2.8 Effects on the Environment............................................................................8
3.0 Assessment of "Toxic" Under CEPA .....................................................................9
3.1 Entry...............................................................................................................9
3.2 Exposure.........................................................................................................9
3.3 Effects...........................................................................................................10
3.3.1 Human health...................................................................................10
3.3.2 Environment.....................................................................................12
3.4 Conclusions ..................................................................................................12
3.4.1 Effects on the environment (Paragraph 11 (a))...............................12
3.4.2 Effects on the environment on which human
life depends (Paragraph 11 (b)).......................................................12
3.4.3 Effects on human health (Paragraph 11 (c)) ...................................13
3.4.4 General conclusions.........................................................................13
4.0 Recommendations for Research and Evaluation.................................................14
5.0 References...............................................................................................................15

v
Overview of Findings
Methyl tertiary-butyl ether (MTBE) is used in Canada as an octane enhancer in gasoline.
Methyl tertiary-butyl ether can enter the environment at any stage in the production, storage, and
transport of undiluted MTBE or MTBE-blended gasoline. Although data on concentrations of
MTBE in the environment are not available, modelling of the fate of MTBE has provided
predictions for concentrations of MTBE in the various media to which humans and other organisms
may be exposed.
The highest concentrations of MTBE predicted in surface water in Canada are at least eight
orders of magnitude lower than the concentration that induces adverse effects in fathead minnow,
the most sensitive aquatic species identified. The effect levels reported in inhalation studies
conducted on laboratory mammals are considered relevant to wild mammals. The highest predicted
atmospheric concentration is at least seven orders of magnitude lower than the lowest reported
effect level in a subchronic inhalation study in mammals.
Because of its low rate of release, its short persistence in the atmosphere, and the resulting
low concentrations of MTBE in the atmosphere, MTBE is not associated with depletion of
stratospheric ozone or with global warming, and is not expected to contribute significantly to the
formation of ground-level ozone.
Based on predicted concentrations of MTBE in ambient air and water and limited
information on concentrations in shellfish, the total average daily intakes of MTBE have been
estimated for various age groups in the general population. These estimates are much less (by
approximately 45 000 times) than the intake to which it is believed that a person can be exposed
over a lifetime without deleterious effect, i.e., the Tolerable Daily Intake derived on the basis of
data from bioassays in animal species.
Based on these considerations, the federal Minister of the Environment and the federal
Minister of Health and Welfare have concluded that the predicted concentrations of MTBE
in the environment in Canada do not constitute a danger to the environment or to the
environment on which human life depends, or to human life or health. Therefore, MTBE is
not considered to be "toxic" as defined under Section 11 of the Canadian Environmental
Protection Act.

1
1.0 Introduction
The Canadian Environmental Protection Act (CEPA) requires the federal Minister of the
Environment and the federal Minister of Health and Welfare to prepare and publish a Priority
Substances List that identifies substances, including chemicals, groups of chemicals, effluents, and
wastes that may be harmful to the environment or constitute a danger to human health. The Act
also requires both Ministers to assess these substances and determine whether they are "toxic" as
defined in Section 11 of the Act which states:
“...a substance is toxic if it is entering or may enter the environment in a quantity or
concentration or under conditions
(a) having or that may have an immediate or long-term harmful effect on the
environment;
(b) constituting or that may constitute a danger to the environment on which
human life depends; or
(c) constituting or that may constitute a danger in Canada to human life or health."
Substances that are assessed as "toxic" according to Section 11 may be placed on Schedule I
of the Act. Consideration can then be given to developing regulations, guidelines, or codes of
practice to control any aspect of these substances' life cycle, from the research and development
stage through manufacture, use, storage, transport, and ultimate disposal.
The assessment of whether methyl tertiary-butyl ether (MTBE) is "toxic", as defined in
CEPA, was based on the determination of whether it enters or is likely to enter the Canadian
environment in a concentration or quantities or under conditions that could lead to exposure of
humans or other biota at levels that could cause adverse effects.
Data relevant to the assessment of the entry, environmental exposure, and environmental
effects of MTBE were obtained from searches of electronic databases between 1989 and 1991.
These databases included: BIOSIS Previews, Chemical Evaluation Search and Retrieval System
(CESARS), Chemical Abstracts, Environment Canada Departmental Library Catalogue (ELIAS),
FATERATE, Federal Register, International Register of Potentially Toxic Chemicals (IRPTC),
National Technical Information Service (NTIS), Pollution Abstracts, Registry of Toxic Effects of
Chemical Substances (RTECS), SOLUB, TOXLINE, and the Toxic Releases Inventory Data Base.
Additional information was obtained from members of the Canadian Petroleum Products Institute
(CPPI) and other representatives of the petroleum industry and from C.S. Liu of Alberta
Environment. Trade information, including production, import, storage, and use data, was obtained
from industry through a mandatory request for information under CEPA, Section 16.
Although much of the research on MTBE has been conducted

2
outside Canada, available Canadian data on sources, use patterns, fate, and effects of MTBE on the
Canadian environment were emphasized.
To identify data relevant to the estimation of exposure of the general human population to
MTBE, several commercial databases were searched from the early 1970s to July 1991. These
included: Environmental Bibliography, ENVIROLINE, Pollution Abstracts, ELIAS, AQUAREF,
BIOSIS Previews, MICROLOG, Cooperative Documents Project (CODOC), Integrated Risk
Information System (IRIS), and Chemical Hazard Response Information System (CHRIS).
To identify toxicological data relevant to the assessment of effects on human health, on-line
literature searches were conducted in June 1991 on the following databases: Hazardous Substances
Data Bank, RTECS, TOXLINE, TOXLIT, Federal Register, and NTIS. Additional relevant
information was obtained from the Canadian Petroleum Products Institute, the MTBE Health
Effects Testing Task Force (a committee of American producers and users of MTBE overseeing
toxicological testing of MTBE), and the United States Environmental Protection Agency (U.S.
EPA). Non-validated studies of Industrial Bio-Test Laboratories Inc. have been cited in this report
but are not used in assessing whether MTBE is "toxic" under CEPA.
Data relevant to the assessment of whether MTBE is "toxic" to human health obtained after
the completion of the human health-related sections of this report (i.e., October 1991) were not
considered for inclusion. Similarly, data relevant to the assessment of whether MTBE is "toxic" to
the environment obtained after April 1992 have not been considered.
Review articles were consulted where appropriate. However, all original studies that form
the basis for determining whether MTBE is "toxic" under CEPA have been critically evaluated by
the following Environment Canada staff (entry, and environmental exposure and effects) and
Health and Welfare Canada staff (human exposure and effects on human health):
Environment Canada Health and Welfare Canada
A. Bobra G. Long
D. Caldbick M.E. Meek
R. Chénier S. Savard
M. Hanlon
K. Lloyd
C. B. Prakash
In this report, an overview of findings concerning MTBE that will appear in the Canada
Gazette is presented. Section 2.0 is an extended summary of the technical information that is
critical to the assessment. This information is presented in greater detail in a Supporting Document
that is available upon request. The assessment of whether MTBE is "toxic" under CEPA is
presented in Section 3.0.

3
The human health-related sections of the Supporting Document and/or Assessment
Report were reviewed externally by S. Ridlon, Chairman of the MTBE Health Effects
Testing Task Force, and British Industrial Biological Research Association (BIBRA) Toxicology
International. These sections were then approved by the Standards and Guidelines Rulings
Committee of the Bureau of Chemical Hazards of Health and Welfare Canada. Environmental
components of the Supporting Document were reviewed externally by G. Grappolini, Petro-Canada
Products, on behalf of the Canadian Petroleum Products Institute, and by C. S. Liu from Alberta
Environment. The final Assessment Report was reviewed and approved by the Environment
Canada/Health and Welfare Canada CEPA Management Committee.
Copies of this assessment report and of the unpublished supporting document are available
upon request from:
Commercial Chemicals Branch
Environment Canada
14th Floor, Place Vincent Massey
351 St. Joseph Boulevard
Hull, Quebec
K1A 0H3
Environmental Health Centre
Health and Welfare Canada
Room 104
Tunney's Pasture
Ottawa, Ontario
K1A 0L2

4
2.0 Summary of Critical Supporting Data
2.1 Identity and Physical/Chemical Properties of Substance
Methyl tertiary-butyl ether (CAS Registry Number 1634-04-4) is an aliphatic ether with
structural formula CH3OC(CH3)3. It is a volatile, clear, flammable, colourless liquid at room
temperature, and has a terpene-like odour. Methyl tertiary-butyl ether is miscible in gasoline and
soluble in water, alcohol, and ether. It has a relatively high vapour pressure (3.35 x 104 Pa at 250
C)
(Ambrose et al., 1976), a high water solubility (4.8x 104 mg/L at 200
C) (Merck & Co., Inc., 1989)
and a low log octanol/water partition coefficient (1.3) (Veith et al., 1983).
Methyl tertiary-butyl ether is produced by reacting isobutylene with methanol over an acid
catalyst. Common analytical methods used to quantify MTBE include gas chromatography with
mass spectrometry, flame ionization, or an oxygen specific response flame ionization detector.
2.2 Production and Uses
The first plant ever to produce MTBE in Canada began operating in 1992 in an industrialized
area of Edmonton, Alberta. The plant is to produce an estimated 500 000 tonnes of MTBE per year,
most of which is intended for export to the United States. The MTBE will be shipped by rail from
Edmonton to Kitimat, British Columbia and from there it will be shipped by ocean tanker
(Solsberg, 1991).
From 1986 to 1990, Canada imported between 7000 and 25 000 tonnes/year of MTBE for
the purpose of blending as an octane enhancer in unleaded gasoline. Most of the imports entered
Ontario and Quebec, and smaller amounts went to Alberta and British Columbia. Over the next five
years, it is estimated that importation will increase to approximately 38 000 tonnes/year. Assuming
that Canada's overall consumption of gasoline will not change appreciably over the next four years,
it is estimated that MTBE-blended gasolines will continue to account for approximately 2% of the
total unleaded gasoline in Canada, as it has during the past five years. The average concentrations
of MTBE in these blended gasolines range from 6.5 to 9.6% by volume (Environment Canada,
1991).
Worldwide production of MTBE has increased dramatically since 1979, when it
was approved in the United States and other countries for use in gasoline. In western
Europe, unleaded gasoline can contain 10 to 15% MTBE by volume. In the
United States, concentrations of up to 15% MTBE by volume in unleaded gasoline have
been approved by the U.S. EPA. Methyl tertiary-butyl ether is currently among the 50
highest production volume chemicals in the United States. Total production of MTBE in
the United States was estimated to be 3 200 000 tonnes/year (Chemical Market Reporter,
1990). World production capacity in 1989 was 7 425 000 tonnes and is projected to rise
to 19 413 000 tonnes/year by 1994. The growing demand for MTBE as a
gasoline-blending component results from the expanded market for high octane unleaded

5
gasolines, and the increased pressure to reduce evaporative emissions, carbon monoxide (CO)
emissions, and the aromatic contents of gasoline (Prakash, 1989).
2.3 Sources and Releases
Methyl tertiary-butyl ether can enter the environment at any stage in the production, storage,
and transport of undiluted MTBE or MTBE-blended gasoline. The largest environmental releases
are through fugitive emissions from chemical manufacturing plants, gasoline terminals, service
stations, and from spills (U.S. EPA, 1986). No data are available on releases of MTBE from engine
combustion of MTBE-blended gasoline. Canadian data on environmental releases are not available.
Releases of MTBE from ten plants in the United States have been estimated to range from 0.003 to
0.07% of the total MTBE used or produced, with an average of 97% of released MTBE being
emitted into air, 1.7% into water, and 1.3% into soil (TOXNET-TRI, 1991). Assuming that 0.07%
of all the projected production of MTBE at the Edmonton plant would be released into the
environment in similar proportions, this would result in annual releases of 340 tonnes of MTBE
into the air, 6 tonnes into water, and 5 tonnes into soil.
2.4 Environmental Fate and Concentrations
2.4.1 Fate
Mechanisms affecting the environmental fate of MTBE include photo-oxidation (Japar et al.,
1990; 1991), volatilization (Thomas, 1982), and biodegradation (Fujiwara et al., 1984). In the
environment, MTBE should be found primarily in the atmosphere and in water because of its
relatively high vapour pressure, high water solubility, and low octanol/water partition coefficient.
Based on measured rate constants for reactions with hydroxyl radicals in air, the photo-
oxidation half-life for MTBE has been estimated to be between 20.7 and 265 hours (Atkinson,
1985; Wallington et al., 1988). The atmospheric oxidation of MTBE produces tertiary-butyl
formate (major product), 2-methoxy-2-methyl propanal, and other minor products (Japar et al.,
1991). In water, biodegradation appears to be the only degradation process of any significance. The
half-life of MTBE was estimated to be between 28 and 180 days for aerobic biodegradation in
surface waters and between 112 and 720 days for anaerobic biodegradation in deep water or
groundwater (Fujiwara et al., 1984). Based on physical/chemical properties, the half-life for
volatilization of MTBE from surface waters to the atmosphere was estimated to be 9 hours (U.S.
EPA, 1986).
2.4.2 Concentrations
No information was found in the literature on MTBE concentrations in air, surface waters,
groundwater, soil, or sediment in Canada. In a study carried out in Nova Scotia for the detection of
organic and inorganic contaminants in shellfish, MTBE was not detected (detection limit of 0.01
µg/g) in 21 samples that were assayed (Environment Canada, 1989).

6
Concentrations of MTBE in ground-level air at three refineries in the United States were less
than 30 µg/m3
(API, 1989). Trace quantities of MTBE (5 ng/L) were detected in estuarine water
and sediment samples adjacent to motorways and centres of heavy urban road traffic in the United
Kingdom (Bianchi and Varney, 1989).
There have been several incidents of MTBE being detected in groundwater in areas where
underground storage tanks containing MTBE-blended gasoline have leaked. In some of these
incidents in the United States, MTBE concentrations ranged from 1.96 µg/L to 236 mg/L (Garrett,
1987). When present in groundwater at high concentrations, MTBE can act as a cosolvent and
enhance the mobility of other gasoline components (Rao et al., 1990; Garrett et al., 1986).
Bioconcentration of MTBE in aquatic biota is not significant. Whole body, steady-state
bioconcentration factors (BCF) of 1.1 and 1.08 have been reported for carp, Cyprinus carpio
(Fujiwara et al., 1984). Fish exposed for 28 days and then transferred to clean water eliminated
almost all of the MTBE residues within 3 days (Fujiwara et al., 1984). Concentrations in fish
would therefore be expected to be close to the concentrations in water.
Because of the lack of data on the behaviour of MTBE in the Canadian environment,
estimates of fate and concentrations of MTBE in the environment were generated using the Level
III Fugacity Computer Model of Mackay and Paterson (1991) developed for southern Ontario.
Based on estimates for import into southern Ontario (Environment Canada, 1991) and data on
releases in the United States (TOXNET-TRI, 1991), it was assumed that MTBE would be released
into the environment at rates of 119 mol/hour into air, 3.6 mol/hour into water, and 0.6 mol/hour
into soil. Modelling indicated that at steady-state, 56.2% MTBE would be found in the air, 43.3%
in surface water, <0.01% in sediment, and 0.5% in soil. This would result in steady-state
concentrations of 1.5 ng/m3
in air, 0.12 ng/L in water, 0.28 ng/kg (dry weight) in soil, and 0.068
ng/kg (dry weight) in sediment.
A release of 1% of the total estimated 1992 Canadian production of
500 000 tonnes/year would result in emissions and concentrations approximately
50 times greater than those estimated in the previous paragraph. The 1% release was
chosen to represent a worst-case scenario, corresponding to approximately ten times the
estimated maximum United States emission rate from chemical plants.
2.5 Toxicokinetics and Metabolism
Methyl tertiary-butyl ether appears to be rapidly and completely absorbed from the
gastrointestinal tract of rats, whereas absorption following dermal exposure is limited (Bio-
Research Laboratories Ltd., 1990a). Following oral, inhalation, dermal, or intravenous exposure in
experimental animals, MTBE is rapidly eliminated unchanged, or as metabolites, principally
tertiary-butanol in expired air and tertiary-butanol, 2-methyl- 1,2-propanediol and alpha-
hydroxyisobutyric acid in urine (Savolainen et al., 1985; Exxon Biomedical Sciences, Inc., 1988;
Bio-Research Laboratories, Ltd. 1990a; 1990b; 1990c; 1990d).

7
Available data indicate that accumulation of MTBE and/or metabolites following repeated
exposure by inhalation is unlikely (Bio-Research Laboratories Ltd., 1990c) and that the metabolism
of MTBE to tertiary-butanol may be saturated at high doses (Bio-Research Laboratories Ltd.,
1990a; 1990b; 1990d). Methyl tertiary-butyl ether and its metabolite tertiary-butanol have been
detected in the blood, urine, fatty tissue, and mothers' milk of patients undergoing gallstone
treatment by transhepatic gallbladder litholysis using MTBE (Leuschner et al., 1991).
2.6 Mammalian Toxicology
The acute toxicity of MTBE is low following inhalation, oral, or dermal administration. The
oral (gavage) LD50 in male and female albino rats is approximately 3.8 g/kg b.w. (Industrial Bio-
Test Laboratories, Inc., 1969; ARCO Chemical Co., 1980). Reported LC50s in rats for 4-hour
inhalation exposures to MTBE are 85 g/m3
(Industrial Bio-Test Laboratories, Inc., 1969) and 120
g/m3
(ARCO Chemical Co., 1980). Methyl tertiary-butyl ether did not induce dermal sensitization
in guinea pigs (ARCO Chemical Co., 1980).
Short-term repeated dose toxicity studies for MTBE are limited to a two-week inhalation
study in small groups of rats and monkeys (Industrial Bio-Test Laboratories, Inc., 1970a; 1970b), a
nine-day inhalation study in rats (Bio/dynamics Inc., 1984) and a 14-day study in which the
compound was administered orally by gavage to rats (Robinson et al., 1990). At high
concentrations (> 1020 ppm; > 3731 mg/m3
), inhalation of MTBE induced clinical signs of eye
irritation and chronic inflammatory changes in the nasal mucosa and trachea (Bio/dynamics Inc.,
1984) and profound anaesthesia following ingestion of 1428 mg/kg b.w. (Robinson et al., 1990).
Decreases in body weight gain have also been observed following ingestion of lower doses (714
mg/kg b.w.) (Robinson et al., 1990).
Subchronic toxicity studies are limited to one oral and three inhalation studies in rats. In an
inhalation study conducted by Greenough et al. (1980), anaesthesia was the only adverse effect
observed in rats at concentrations as low as 250 ppm (915 mg/m3
). However, this effect was not
observed at higher concentrations in a more recent investigation in another strain of rats.
In the most extensive bioassay, Dodd and Kintigh (1989) reported a "no-observed-adverse-
effect-level (NOAEL)" of 797 ppm (2915 mg/m3
), based on neurobehavioural effects observed at
concentrations of 3920 ppm (14 339 mg/m3
) and above. Increases in the relative weights of the
liver and kidney in male rats were observed at this concentration (797 ppm), which might more
appropriately have been considered a lowest-observed-effect-level (LOEL).
Data on the chronic toxicity and potential carcinogenicity of MTBE have not been identified.
However, an oncogenicity study in CD-1 mice and F344 rats is under way and is expected to be
completed in late 1992 (Kneiss, 1991).

8
In four inhalation studies conducted to date, MTBE has not induced developmental effects in
rats, rabbits, or mice at doses below those that were toxic to the mother (Conaway et al., 1985; Tyl,
1989; Biles et al., 1987). Adverse effects on reproduction in the absence of parental toxicity have
not been observed in one- and two-generation studies in rats (Biles et al., 1987; Neeper-Bradley,
1991).
Methyl tertiary-butyl ether has been assayed in several in vitro and in vivo genotoxicity tests
covering a range of genetic endpoints. Although there is no convincing evidence that MTBE is
genotoxic in studies conducted to date, definitive conclusions cannot be reached because of the
limitations of several of the available investigations.
2.7 Effects on Humans
Available data on the toxicity of MTBE to humans are restricted to case reports of adverse
effects following its use as a treatment for gallstones. In general, only mild effects have been
reported, including a faint odour on the breath, nausea, vomiting, drowsiness, and mild
inflammatory changes in the gallbladder following repeated treatment with several millilitres of
MTBE (Allen et al., 1985; Sauerbruch et al., 1985; Murray et al., 1988; Thistle et al., 1989; Van
Sonnenberg et al., 1991). Ponchon et al. (1988), however, noted the potential for adverse effects
from treatment with MTBE, describing a case in which leakage of 15 mL of MTBE resulted in
coma and acute renal failure.
2.8 Effects on the Environment
Few data are available on the toxicity of MTBE to aquatic biota. Data on acute toxicity are
available for one species of invertebrate, four species of fish, and one species of amphibian. The
experimental data ranged from a 96-hour LC50 of 672 mg/L for the fathead minnow, Pimephales
promelas (Geiger et al., 1988), to a 96-hour LC50 of > 10 000 mg/L for a copepod, Nitocra spinipes
(Tarkpea and Svanberg, 1982).
No data are available for toxicity to wild mammals, birds, terrestrial plants, or soil biota. The
toxicity of MTBE to wild mammals can be assessed by extrapolation from the results of toxicity
studies conducted using laboratory mammals (see Section 2.6).
Methyl tertiary-butyl ether is not considered to be a greenhouse gas or to contribute to
stratospheric ozone depletion, since its low rate of release to the atmosphere and its short
atmospheric half-life (less than 12 days) result in very low atmospheric concentrations. Because
MTBE is a volatile organic compound, it could contribute to the formation of ground-level ozone.
The extent of its contribution is not known, but it is believed to be relatively small given the low
concentrations of MTBE in air compared to those of other volatile organic compounds (CCME,
1990).

9
3.0 Assessment of "Toxic" Under CEPA
As described in the Introduction, the following assessment will consider the entry of MTBE
to the environment, the exposure to humans and other biota, and potential harmful effects to
humans and other biota.
3.1 Entry
From 1986 to 1990, Canada imported between 7000 and 25 000 tonnes/year of MTBE for
the purpose of gasoline blending. Approximately 2% of the unleaded gasoline in Canada is blended
with MTBE, which accounts for about 6.5 to 9.6% by volume of the resulting blend. It is expected
that 500 000 tonnes/year will be produced in Canada starting in 1992, with most of this production
being exported. Methyl tertiary-butyl ether can enter the environment at any stage in the
production, storage, use, and transport of MTBE or MTBE-blended gasoline.
The largest environmental releases are likely to occur as fugitive emissions from chemical
manufacturing plants, gasoline terminals, service stations, and spills. Therefore, although data are
not available on the absolute amounts of MTBE entering the Canadian environment and on the
resulting environmental concentrations, it is concluded that MTBE enters the Canadian
environment.
3.2 Exposure
No data are available on environmental concentrations in Canada. Based on steady-state
fugacity modelling, environmental concentrations in southern Ontario are estimated to be 1.5 ng/m3
in air and 0.12 ng/L in water. Under a worst-case scenario, it was assumed that approximately 1%
of the predicted Canadian MTBE production could be emitted to the environment, resulting in
environmental concentrations of 75 ng/m3
in air and 6 ng/L in water.
Human exposure to MTBE is difficult to estimate because of the lack of data on
concentrations of MTBE in ambient and indoor air, drinking water, or in food in Canada, the
United States, and other countries. Based on fugacity modelling, it is estimated that inhalation in
air would be the principal route of exposure {e.g., 35 ng/day based on a predicted concentration of
1.5 ng/m3
and an assumed inhalation volume of air for adults of 23 m3
daily (EHD, 1988)}. Intake
in drinking water would be considerably less {0.18 ng/day based on a predicted concentration of
0.12 ng/L and an assumed volume ingested of 1.5 L daily for adults (EHD, 1988)}. Based on data
available concerning the physical/chemical properties of MTBE and the limited information on
concentrations in shellfish, intake in food is expected to be negligible compared to that inhaled.
It is recognized that there may be additional exposure (including dermal) of the general
population to MTBE at self-serve gasoline stations. Available data, however, are insufficient to
estimate exposure from this source and absorption following dermal exposure appears to be
limited.

10
It is estimated, therefore, that the average daily intake of MTBE for Canadian adults would
not exceed 35 ng/day (<0.5 ng/(kg b.w.·day) for a 70 kg man) (EHD, 1988). For 5- to 11-year-olds,
the age group with greatest predicted exposure on a body weight basis, estimated intake is 0.67
ng/(kg b.w.·day) { assuming average body weight of 27 kg, inhalation volume of 12 m3
/day,
drinking water intake of 0.3 L/day (EHD, 1988), and predicted concentrations of MTBE of 1.5
ng/m3
in air and 0.12 ng/L in water}.
These estimated intakes are based on mean predicted concentrations in the general
environment. Elevated levels, for example, present in groundwater in areas where underground
storage tanks containing MTBE-blended gasoline have leaked, were not considered relevant to
estimation of exposure for the general population.
3.3 Effects
3.3.1 Human health
Limited data are available on the toxicity of MTBE to human health. Epidemiological
studies of exposed populations are not available and information on chronic toxicity or
carcinogenicity in experimental animals has not been identified. An oncogenicity study is in
progress, however, and should be completed within the next few years. Although there is no
convincing evidence that MTBE is genotoxic from in vitro and in vivo studies covering a range of
genetic endpoints, it is not possible to draw definitive conclusions due to the limitations of several
of the available investigations. Methyl tertiary-butyl ether has been classified, therefore, in Group
V (inadequate data to assess) of the classification scheme developed for use in the derivation of the
"Guidelines for Canadian Drinking Water Quality" (EHD, 1989). In studies conducted to date,
MTBE has also not induced adverse reproductive effects in rats or developmental effects in rabbits,
rats, or mice at doses below those that were maternally toxic.
For compounds classified in Group V, a Tolerable Daily Intake (TDI) is derived on the basis
of a no- or lowest-observed (adverse) effect level (NO(A)EL or LO(A)EL) in humans or animals
divided by an uncertainty factor. With the exception of the one- and two-generation studies designed
to specifically investigate reproductive and developmental effects (Biles et al., 1987; Neeper-
Bradley, 1991), the longest term studies of the effects of MTBE are sub-chronic investigations.
Those in which an adequate range of endpoints has been examined are restricted to one oral
(Robinson et al., 1990) and two inhalation studies (Greenough et al., 1980; Dodd and Kintigh, 1989)
in rats. The inhalation studies are the most relevant to this assessment since, based upon
concentrations in air and water predicted by fugacity modelling and a limited amount of information
on MTBE levels in shellfish in Canada, air is expected to be the principal medium of exposure to
MTBE for the general population. In an inhalation study conducted by Greenough et al. (1980),
anaesthesia was the only adverse effect observed in rats at concentrations as low as 250 ppm (915
mg/m3
). However, this effect was not observed at higher concentrations in a more recent, extensive
investigation on another strain of rats (Dodd and Kintigh, 1989). This was the most extensive
subchronic study in which there was assessment of neurobehavioural effects and histopathological
examination of the nervous system, in addition to traditional endpoints in groups exposed

11
examination of the nervous system, in addition to traditional endpoints in groups exposed to three
concentrations and controls. The "NOAEL" in this study was considered to be 797 ppm (2915
mg/m3
) based on neurobehavioural effects, including increased body temperature in female rats,
decreased hind limb grip in males, and increased motor activity in females observed at the next
highest concentration. However, increases in the relative weights of the liver and kidney in males
were recorded at 797 ppm (2915 mg/m3
). It might be more appropriate, therefore, to consider this
concentration as a LOEL. On the basis of this "NOAEL", a Tolerable Daily Intake (TDI) is
conservatively (owing to the paucity of available data), derived as follows:
TDI = 2915 mg/m3
x (6/24) x (5/7) x 0.144 m3
/d
10 000 x 0.25 kg
= 75.5 mg/ (kg b.w.·day)
2500
= 0.030 mg / (kg b.w.·day) which is: 30 µg / (kg b.w. · day)
or 30 000 ng/ (kg b.w. · day)
where:
2915 mg/m3
= the "NOAEL" in the most extensive sub-chronic study by the most
appropriate route of exposure (i.e., inhalation) conducted to date (Dodd
and Kintigh, 1989)
6/24 and 5/7 = conversion of dosing for 6 hours/day, 5 days/week to continuous exposure
0.144 m3
/day = assumed inhaled air volume of adult rats (Altman and Dittmer, 1972)
0.25 kg = assumed body weight of adult rats (NIOSH, 1985)
10 000 = uncertainty factor (x 10 for intraspecies variation; x 10 for interspecies
variation; x 10 for less than chronic study; x10 for lack of data on
carcinogenicity and chronic toxicity and minimal effects - increases in
liver and kidney weights in males - observed at the "NOAEL" in the
critical study)
In the two-generation reproductive toxicity study conducted by Neeper-Bradley
(1991), clinical signs and transient reductions in body weight were observed in F0 and F1
animals exposed to 3000 ppm (10 974 mg/m3
). Based on these results, the NOEL was
considered to be 400 ppm (1463 mg/m3
), which is slightly less than the "NOAEL" from
the subchronic study (Dodd and Kintigh, 1989) used here in the derivation of the TDI.
However, the assessment of neurobehavioural effects and histopathological examination

12
3.3.2 Environment
Very few data are available on the toxicity of MTBE to aquatic biota. The most sensitive
species identified was the fathead minnow, with a 96-hour LC50 of 672 mg/L.
No data are available for toxicity of MTBE to wild mammals, birds, terrestrial plants, or soil
biota. The effect levels reported in inhalation studies conducted on laboratory animals are
considered relevant to wild mammals. The lowest reported effect level was 797 ppm (2915 mg/m3
)
for rats under conditions of subchronic (13-week) exposure by inhalation.
3.4 Conclusions
Methyl tertiary-butyl ether is used in Canada for gasoline blending and is produced for
export. Both sources can lead to entry of MTBE into the Canadian environment. This entry results
in concentrations of MTBE that may be estimated for the various media to which humans and other
organisms are exposed.
3.4.1 Effects on the environment (Paragraph 11 (a))
The concentration of MTBE in surface water predicted under a worst-case scenario (6 ng/L)
is 1.12x 108 times lower than the 96-hour LC50 for the fathead minnow (672 mg/L).
The highest predicted airborne concentration of MTBE (75 ng/m3
) is 3.9 x 107 times lower
than the lowest reported effect level in a subchronic inhalation study in rats (2915 mg/m3
).
Given the low predicted concentrations of MTBE in the environment and the lack of
bioaccumulation, concentrations in food for wildlife are expected to be at least several orders of
magnitude lower than those causing acute toxicity. In addition, given the low toxicity of MTBE to
aquatic organisms, wildlife food sources are not expected to be at risk due to environmental
concentrations of MTBE.
Therefore, on the basis of available data, MTBE is not considered to be
"toxic" as defined under Paragraph 11 (a) of CEPA.
3.4.2 Effects on the environment on which human life depends (Paragraph 11 (b))
Due to its low rate of release and its short persistence in the atmosphere, MTBE is not
expected to be involved in global warming or in the depletion of stratospheric ozone. The
contribution of MTBE to the formation of ozone in the lower atmosphere is believed to be
relatively small because of its low predicted atmospheric concentrations.
"toxic" as defined under Paragraph 11 (b) of CEPA.

13
3.4.3 Effects on human health (Paragraph 11 (c))
It is difficult to estimate exposure of the Canadian population owing to the lack of data on
concentrations of MTBE in ambient and indoor air, drinking water, or food. Based on fugacity
modelling and limited information on concentrations in shellfish, it is estimated that the average
daily intake of MTBE for the age group of the Canadian population most exposed on a body weight
basis (i.e., 5- to 11-year-olds) is 0.67 ng/(kg b.w.·day). Although not based on actual data on
concentrations in air, water or food, this estimated average daily intake is considerably less (by
approximately 45 000 times) than the Tolerable Daily Intake previously derived.
"toxic" as defined under Paragraph 11 (c) of CEPA.
3.4.4 General conclusions
"toxic" as defined under Paragraphs 11 (a), (b) and (c) of CEPA.

14
4.0 Recommendations for Research and Evaluation
1. Given the almost total absence of data on environmental concentrations in
Canada, concentrations of MTBE in air, water, groundwater, soil, and biota
should be monitored in areas adjacent to major sources, including MTBE
production and storage facilities, service stations, and areas of high vehicle
traffic. This research is considered to be of medium priority.
2. Long-term toxicity tests should be undertaken using aquatic and terrestrial
organisms. This research is considered to be of low priority.
3. When available, the results of the ongoing carcinogenicity bioassay and
data on concentrations of MTBE in ambient air in Canada should be
assessed with respect to their implications for a possible designation of
"toxic" under the Act. This assessment is considered to be of high priority.

15
5.0 References
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(1990b).

16
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14
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Industry Conducted by the Commercial Chemicals Branch, March 20. Environment Canada,
Commercial Chemicals Branch, Ottawa (1991).

17
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Ethers", Yukagaku, 33(2), 111-114 (1984).
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N8970. Northbrook, Illinois (1970b).
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Oxygenated Organic Compounds", Environ. Sci. Technol. 25, 415-420 (1991).

18
Kneiss, J., "An Overview of the MTBE Toxicology Testing Program", presented at the National
Conference on Octane Markets and Reformulated Gasoline, March 19-21, 1991, San Antonio,
Texas (1991).
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M. Leuschner, "Gallstone Dissolution with Methyl tert-butyl Ether in 120 Patients -Efficacy
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19
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